Improvements in the thermal stability and flame retardant character of textile structures have become necessary to provide protective clothing suitable for use under the potentially adverse thermal conditions which may be encountered in, e.g., the operation of jet aircraft. As noted by van Krevelen in Die Angewandte Makromolekulare Chemie 22 (1972), 133-157 (Nr. 300), one aspect of the progress made in the search for heat resistant and nonflammable materials has been the development of highly cyclic polymers, both aromatic and heterocyclic, among them being the aromatic polyamides.
Methods indicated as useful for imparting greater heat resistance and reduced flammability to fibers and fabrics prepared from aromatic polyamides have been reported. However, these processes (e.g., semicarbonization, sulfuration, halogenation, and metallization) yield products possessing certain properties which tend to limit their broad applicability as textile materials. An obvious limiting property is the range of colors exhibited by the treated textile structures. These colors are variously identified to be, e.g., "darkened", dark brown, red-brown, blue-black, black, and reddish. A second limitation in these modified aromatic polyamides is the reduced elongation value exhibited by the treated fiber; it is acknowledged that such fibers cannot be converted as easily into woven fabrics or other shaped articles as can be the untreated fiber. It is recommended that the aforementioned prior art treatments be performed upon shaped articles (e.g., woven fabric) formed from the untreated fiber. Thus, both aesthetic appeal and processability of the treated fiber are diminished by these limitations. In addition, in order to achieve the desired transformation of the untreated products, it is indicated that the treatment processes need to be run under carefully controlled, critical conditions of time and temperature (elevated), features which can lead to significantly increased cost for the final product.